Re: Re: [PATCH v8 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace

On Tue, Jun 29, 2021 at 11:29 AM Jason Wang [off-list ref] wrote:

在 2021/6/29 上午10:26, Yongji Xie 写道:

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On Mon, Jun 28, 2021 at 12:40 PM Jason Wang [off-list ref] wrote:

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在 2021/6/25 下午12:19, Yongji Xie 写道:

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2b) for set_status(): simply relay the message to userspace, reply is no
needed. Userspace will use a command to update the status when the
datapath is stop. The the status could be fetched via get_stats().

2b looks more spec complaint.

Looks good to me. And I think we can use the reply of the message to
update the status instead of introducing a new command.

Just notice this part in virtio_finalize_features():

          virtio_add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK);
          status = dev->config->get_status(dev);
          if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) {

So we no reply doesn't work for FEATURES_OK.

So my understanding is:

1) We must not use noreply for set_status()
2) We can use noreply for get_status(), but it requires a new ioctl to
update the status.

So it looks to me we need synchronize for both get_status() and
set_status().

We should not send messages to userspace in the FEATURES_OK case. So
the synchronization is not necessary.

As discussed previously, there could be a device that mandates some
features (VIRTIO_F_RING_PACKED). So it can choose to not accept
FEATURES_OK is packed virtqueue is not negotiated.

In this case we need to relay the message to userspace.

OK, I see. If so, I prefer to only use noreply for set_status(). We do
not set the status bit if the message is failed. In this way, we don't
need to change lots of virtio core codes to handle the failure of
set_status()/get_status().

Thanks,
Yongji